[Koha] How to show description of authorized value in facet?

[Michael Kuhn]

Hi

Environment: Debian GNU/Linux 8 with Koha 16.11.04 (package installation)

Our Koha catalogue contains MARC field 385 $a with content e. g. "KG", 
linked to category "Lesekategorie" containing authorized values for the 
target audience, e. g. value "KG" (description for staff client and OPAC 
is: "Kindergarten"). Instead of "KG" the OPAC shows "Kindergarten" as 
expected.

Now I have recently added a new facet for MARC field 385 $a and the 
facet does show - only instead of the description ("Kindergarten"), the 
facet shows the authorized value "KG". How can it be achieved to show 
the description in the facet?

As I see it is actually possible to show the description because the 
authorized values for standard category "LOC" are properly showing the 
descriptions. I tried to find out how this works in file 
"opac-facets.inc" but without success. Can anyone please give me a hint?

Best wishes: Michael